How do alternative bearing surfaces influence wear behavior?

Metal, ceramic, and polyethylene liners represent contemporary bearing choices for total joint replacement. Each has limitations in terms of design, sensitivity to manufacturing, and surgical placement. With polyethylene, larger femoral heads represent a design restriction and a potential wear issue. One side benefit is that polyethylene does not click, squeak, or create stripe wear. The attraction of hard-on-hard bearings (metal-on-metal, ceramic-on-ceramic) is that their typically ultra-low wear alleviates concerns with large femoral head designs. However, hard-on-hard bearings produce stripe wear due to the effects of the rigid liner edge. Slight subluxation (microseparation) during swing phase of gait can result in stripe wear on the ball and liner rim. In addition, high levels of implant wear with vertically placed cups can be anticipated. Currently, only alumina-on-alumina bearings can claim virtually no biologic risk. Thus, the role of laboratory studies is to isolate relevant aspects of performance by cup design and to predict the risk-benefit ratios in patients requiring total hip replacement.